1. Field of the Invention
The present invention relates to nonoxidative hair colorants based on certain anionic polymethine dyes and to a method for temporary hair coloration whereby the coloration can be removed at any time.
The coloring of hair is currently subject to the most varied trends. Whereas in the past hair was colored primarily to cover gray areas, today there is an increasing demand for integrating the hair color into current fashion as an expression of personality.
Now as before, two established methods of hair coloring are available. One of these is the oxidative hair coloring which a priori is unsuitable for temporary coloring, because it produces a very durable coloring result. The other method consists of the possibility of coloring hair with colorants containing nonoxidative, direct dyes (often referred to as toners). Although the dyes used for this purpose are optimized for dyeing performance as well as for remaining on the hair as long as possible, the color shade gradually fades with every hair washing. Thus, depending on the product used and the type of hair, such colorations as a rule do not last more than a maximum of 10 hair washings. If the user of such nonoxidative colorants would like to restore her original hair color at an earlier time, no satisfactory means are currently available for rapidly restoring the original color, because the products used for this purpose are usually very aggressive causing hair damage.
2. Prior Art
In the literature are described many attempts to restore the color of fibers. For example, German Patent DE 38 42 74 and U.S. Pat. No. 4,681,471 describe the decoloration of triarylmethane dyes with reducing agents. U.S. Pat. No. 5,474,578 uses the same approach based on the use of oxidative or reductive decoloration or a combination of these two treatments. A general problem underlying these methods is, in particular, that in most cases only partial decoloration is attained. Thus the method of U.S. Pat. No. 5,474,578 in the most favorable case produces a maximum degree of decoloration of 90 to 93%, and this degree of decoloration can be achieved only by applying a reductive treatment after an oxidative one. Such double treatment, however, causes extraordinary hair damage. Normally, such a method produces only partial (often &lt;50%) hair decoloration.
The foregoing patents also have in common that they deal with the decoloration of dye classes that have been used in hair cosmetics for a long time. The colorants are based on direct dyes with different chemical and physical properties and with different coloring and bleaching characteristics. Hence, at least for color shading that requires dye mixtures, it is very difficult to produce uniform decoloration, because the result is determined by the properties of the least active component.
Hence, a need exists for nonoxidative colorants that can be removed at any time without causing major hair damage.
Some of the polymethine dyes and their suitability for the coloring of fibers have been known for a long time. A review of these dyes can be found, for example, in Houben-Weyl 5/1d, 4th edition (1954) page 227 ff. Some of these polymethine dyes are also commercially available. Although in some cases good to satisfactory coloring results are obtained, a complete removal of such dyes is usually very difficult. Thus pentamethine isooxazolone dyes produce a coloration, but the removal of this coloration is possible only to an insufficient degree.